EP1682803A1

EP1682803A1 - Tube for the transport of particularly powdery materials generating an electrostatic charge

Info

Publication number: EP1682803A1
Application number: EP04761934A
Authority: EP
Inventors: Rudolf Wenger; Peter Waibel; Werner Zimmermann
Original assignee: Huber and Suhner AG
Current assignee: Huber and Suhner AG
Priority date: 2003-11-12
Filing date: 2004-09-21
Publication date: 2006-07-26
Also published as: WO2005047748A1; US20070144756A1

Abstract

The invention relates to a tube, for the transport of particularly powdery materials generating an electrostatic charge, comprising an inner chamber (14), enclosing tube walls (12), defined in the direction of the inner chamber (14) by means of an inner surface (13), whereby the tube wall (12) is made from a flexible base material with poor or no electrical conductivity with an integrated electrical conducting element (17, 18), running in the longitudinal direction of the tube for removal of electrical charges from the tube wall (12). According to the invention, an improved removal of the charges without affecting the conventional tube properties may be achieved, whereby at least one region (12) of the tube wall (12) adjacent to the inner chamber (14) of the tube, has a higher electrical conductivity than the base material and the at least one electrical conducting element (17, 18) is directly connected to the region of increased electrical conductivity (12).

Description

DESCRIPTION

HOSE FOR CONVEYING ELECTROSTATIC CHARGES, IN PARTICULAR POWDERED MEDIA

TECHNICAL AREA

The present invention relates to the field of conveyor technology. It relates to a hose for conveying electrostatic charges, in particular powdery media, according to the preamble of claim 1.

STATE OF THE ART

In powder coating, a powder-air mixture is usually supplied to a spray gun via a feed line. The powder particles emerge from the gun as electrically charged particles and are deposited from a powder cloud on the surface of the workpiece to be coated. The workpiece is closed grounded for this purpose. The powder particles can be positively or negatively charged depending on the technology used. A negative charge of the powder particles is achieved, for example, by a high-voltage electrode arranged at the gun outlet (so-called “corona charging”). A positive charge of the powder particles can be achieved by a suitable powder

Frictional charging can be generated in the powder tube of the gun (so-called "tribo-charging").

The powders used in powder coating (e.g. paint powder) are conveyed from hoses to the spray gun using hoses using cleaned compressed air. Transparent plastic hoses are used as hoses, which are flexible and kink-resistant and enable optical monitoring of the conveying process.

Due to the friction of the powder particles of the conveyed powder-air mixture on the walls of the hoses consisting of electrically insulating material, static electrical charges are built up on the hose walls, which cannot flow away without special precautions. Such charges can lead to breakdowns in the hose area, which damage the hose and possibly cause it to leak, and also entail the risk of ignition of the conveyed material.

Undesired charging processes in the delivery hoses are not limited to powder-air mixtures from powder coating systems, but occur in many other areas where powdery substances, but also liquids (e.g. fuels) are conveyed in electrically insulating hoses.

A large number of proposals have therefore been made in the past to solve the problem of static electrical charging when conveying a wide variety of media by means of hoses. All of these suggestions contain measures that can be taken on the hose wall dissipating electrical charges can be dissipated and thus made harmless.

US-A-5, 170,011 discloses a fuel hose consisting of two concentric jackets, in which either a longitudinally extending, electrically conductive strip is provided for discharging electrical charges, which is embedded in the wall of the inner jacket and in a radial direction Direction extends through the wall of the inner jacket (Fig. 1), or a concentric layer of electrically conductive material is arranged on the inner surface of the inner jacket (Fig. 2). However, the entire inner jacket can also be made electrically conductive (column 5, lines 27-51). In all cases, the electrical conductivity is achieved by using carbon black, although reference is made to the possibility of other conductive additives.

From US-A-3,473,087 and GB-A-1, 041, 255 tubes or polytetrafluoroethylene (PTFE) hoses for the conveyance of liquids, in particular fuels, are known, which are produced from a preform, the two concentric areas comprises, the inner of which has been made electrically conductive by the addition of carbon black, while the outer remains electrically insulating. The hoses produced in this way have a comparatively thin-walled, concentric inner region which is electrically conductive due to the soot additive and which can be used to discharge static electrical charges. By restricting the addition of carbon black to the interior, in one case (GB-A-1, 041, 255) the transparency of the outer tube wall is to be maintained for the purposes of visual inspection of the tube. In the other case (US-A-3,473,087) the resistance of the hose against the so-called "fuel cracking" should be largely retained.

From US-A-3,555,170 it is also known to embed a longitudinally extending conductor strip in a flexible hose made of electrically insulating material for the conveyance of liquids or powders that the shape a fabric made of fine metal wires and elastic yarn. The conductor strip can be arranged on the outside, in the middle of the tube wall, or on the inside.

Finally, EP-A2-0 974 779 describes a hose for conveying flowable substances such as Coating powders disclosed, the wall of which is made of an electrically non-conductive or poorly conductive material. To discharge electrical charges, a wall part made of electrically conductive material is built into the hose wall, which extends radially over the wall cross-section and axially over the length of the hose and essentially has a cross-sectional shape in the form of a sector. The electrically conductive wall part is preferably made of metal wire or metal strand. Alternatively, it can consist of a plastic made conductive by adding carbon. The electrically conductive wall part can run in the axial direction parallel to the axis or helically around the axis.

The known hoses with their devices for discharging electrical charges are alternatively equipped either with an axially continuous concentric layer or an axially continuous concentric area with increased electrical conductivity compared to the base material (US-A-3,473,087; GB-A-1, 041, 255) , or have a localized band-shaped or wire-shaped conductor element which is integrated into the electrically insulating hose wall and extends in the axial direction (US-A-3,555,170; EP-A2-0 974 779). Both alternatives are juxtaposed in US-A-5, 170,011 (Fig. 1 and Fig. 2).

Each of the two alternatives has advantages and disadvantages: If a concentric part of the hose wall is made electrically conductive by adding electrically conductive particles to dissipate the electrical charges, not only the electrical, but also the mechanical and optical properties of this wall part usually change. The higher the percentage of particles, the better the electrical conductivity on the one hand, the more they change but also the other properties. If, for example, carbon black is added as an electrically conductive material, an originally optically transparent hose loses its transparency with increasing carbon black content. As a countermeasure, the thickness of the electrically conductive layer can be reduced, as has been proposed in GB-A-1, 041, 255, but at the same time the line cross section of the electrically conductive area is reduced.

If a conductor tape or a stranded conductor or - as in EP-A2-0 974 779 - a localized electrically conductive wall part is used instead of the concentrically electrically conductive part of the hose wall, the physical properties of the hose remain unchanged over almost the entire hose wall. On the other hand, the limitation of the electrically conductive element to a very small area of the wall cross-section means that the charges which arise on the inner surface of the hose due to friction can only be collected and dissipated very imperfectly over the entire inner circumference.

PRESENTATION OF THE INVENTION

It is therefore an object of the invention to provide a hose for conveying electrostatic charges, in particular powdery media, which overcomes the disadvantages of known solutions and is characterized in particular by an improved discharge of the electrical charges with a reduced change in the hose properties.

The object is achieved by the entirety of the features of claim 1. The essence of the invention is to provide an area of the hose wall adjacent to the interior of the hose with an increased electrical conductivity compared to the base material and the charges collected through this area by at least one electrical conduction element in dissipate in the axial direction, which is directly connected to the area of increased electrical conductivity. The interaction of the area of increased electrical conductivity with the electrical conduction element brings about an effective collection and dissipation of the electrical charges with a change in the other hose properties that is reduced to a minimum. The area of increased electrical conductivity, which strongly influences the hose properties, can make do with comparatively few proportions of an electrically conductive material, because it is only intended to collect the charges on the inner surface of the hose and lead to the line element. The tightly localized electrical conduction element, which has little influence on the hose properties, on the other hand can be equipped with a comparatively high electrical conductivity and thus effect an effective axial derivation without a negative influence on the hose properties

A first preferred embodiment of the hose according to the invention is characterized in that the area with the increased electrical conductivity extends over the entire hose wall, and in that the increased electrical conductivity of the hose wall is caused by particles which are electrically conductive and are embedded in the base material. Such a hose which is uniformly interspersed with electrically conductive particles can be produced particularly easily because it is not necessary to subdivide the hose wall into concentric sections. However, since the particles are distributed over the entire wall thickness of the tube, an increasing proportion of particles results in a relatively large decrease in the optical transparency. This effect is particularly strong if electrically conductive particles in the form of powder, granules, spheres or flakes, such as carbon black, are used, because in this case a higher particle density is necessary in order to achieve continuous electrical conductivity.

A particularly advantageous further development of this embodiment is characterized in that the base material is an optically transparent polymer, in particular PU, PE or PVC, that the particles are short, electrically highly conductive fibers, in particular carbon fibers, are embedded in the base material, and the concentration of the fibers is selected so that the tube wall remains optically transparent in the radial direction. Since the fibers that are crisscross in the base material remain in contact with each other over a greater distance, they can be used to achieve good electrical conductivity even at a relatively low density. With the same electrical conductivity, the hose properties are influenced much less by the fibers than with other particle shapes. About 1 to 3% by weight of carbon fibers or conductive carbon particles (for example carbon black) are preferably mixed into the base material.

In addition, the inclusion of fibers or carbon fibers in the base material of the hose wall has consequences for the surface structure of the hose wall, which are particularly advantageous particularly when using the hose to convey powdery substances. In practice, it has been found that in hoses with a smooth inner surface, the conveyed powder often adheres to the inner surface and then impairs the conveying process. As a countermeasure, the pressure of the compressed air used for conveying and thus the air flow can be increased. However, since cleaned compressed air is relatively expensive, this leads to increased production costs. The effect of powder adhesion, which is associated with a predominantly laminar flow, can also be combated or eliminated by providing the inner surface with a certain surface roughness. The effectiveness of the surface roughness depends strongly on the type and design of the roughness: If the roughness is sharp-edged or jagged, the adhesion of the powder is made difficult, but in this case higher delivery pressures are still necessary.

If, on the other hand, short fibers are embedded in the base material, the embedded fibers on the surface lead to a uniform, easily controllable roughness with strongly rounded bumps, which on the one hand reliably prevents the powder from adhering to the surface, and on the other hand the flow through the hose is only minimally hampered, so that the delivery can be carried out with minimal delivery pressures. If the embedding of the fiber is restricted to an inner partial area of the hose wall, as is the case with an above-mentioned embodiment of the invention, the outer surface of the hose remains smooth because the outer areas of the

Hose wall are free of embedded fibers. This has the main advantage that the hose on the outside can be cleaned particularly easily.

The at least one electrical line element can be designed as a line region embedded in the hose wall with a significantly increased electrical conductivity compared to the base material, the line region recessed in particular being formed in a radial direction through the hose wall.

However, the at least one electrical line element can also be designed as a wire or stranded conductor embedded in the hose wall, the wire or stranded conductor preferably being at a distance from the inner surface of the hose which corresponds to approximately one third of the wall thickness of the hose wall.

Furthermore, in order to produce a certain rotational symmetry, it can be advantageous for the line region or the wire or stranded conductor in the hose wall to run helically in the longitudinal direction around the hose axis.

The properties of the hose wall are particularly little influenced if, according to another embodiment of the invention, the area with the increased electrical conductivity is limited to a concentric inner area of the hose wall adjacent to the inner surface, or if the area with the increased electrical conductivity is concentrated by a Inner jacket arranged inside the hose is formed, the increased electrical conductivity in the inner region or in the inner jacket of the hose wall also preferably in this case due to the base material embedded, electrically highly conductive particles, and the base material is an optically transparent polymer, in particular PU, PE or PVC, as electrically well-conductive particles short, electrically well-conductive fibers, in particular carbon fibers, are embedded in the base material, and the concentration the fibers and / or the thickness of the inner area or

The inner jacket is selected so that the tube wall remains optically transparent in the radial direction. Due to the fact that the area of increased electrical conductivity adjoins the inner surface, not only can the electrical charges arising there be effectively collected and dissipated via the electrical conduction element, but the embedded fibers also provide an inner surface with a controlled and controlled flow conditions optimal surface roughness.

The at least one electrical line element is preferably embodied as a line region let into the hose wall with a significantly higher electrical conductivity than the base material, the let line region preferably being continuous in the radial direction from the outer surface to the inner region or inner jacket.

It is particularly advantageous with regard to structure and dissipation behavior if the at least one electrical line element is designed as a wire or stranded conductor embedded in the hose wall (12), the wire or stranded conductor preferably at the interface between the inner region (20) or the inner jacket and the remaining hose wall runs.

Here, too, the line area or the wire or stranded conductor in the hose wall can run helically in the longitudinal direction around the hose axis.

Another preferred embodiment of the invention is characterized in that the at least one electrical line element is designed as a wire or stranded conductor embedded in the hose wall, that the The wire or stranded conductor is at a distance from the inner surface of the hose, and that the area with the increased electrical conductivity is designed as a local line area enclosing the electrical line element, the increased electrical conductivity of the hose wall preferably being caused by particles which are embedded in the base material and have good electrical conductivity is and the wire or stranded conductor in the hose wall in the longitudinal direction extends helically around the hose axis. The reduced pipe area improves the optical transparency of the hose so that a material flow in the hose can be controlled even better from the outside. Through the design of the surrounding wire or stranded wire

Conduction area, the risk of caking of powder material transported in the hose on the electrically conductive portion of the inner surface can be further reduced.

The line area surrounding the electrical line element can be formed concentrically to the electrical line element in a particularly simple manner.

It is even more favorable if the line area surrounding the electrical line element has a teardrop-shaped cross section which adjoins the interior of the hose with a tip. The selected drop shape of the

Cross section is an optimum between the best possible discharge of the electrostatic charge and the smallest possible conductive surface on the

Inner surface of the hose.

It has proven particularly useful if the base material of the hose is a

Is polyolefin elastomer.

The hose according to the invention can be used with particularly favorable results to promote coating powders. BRIEF EXPLANATION OF THE FIGURES

The invention will be explained in more detail below on the basis of exemplary embodiments in connection with the drawing. Show it

1 is a perspective side view of an exemplary hose as it is used for conveying colored powders or the like.

FIG. 2 shows an enlarged sector-shaped section from the hose wall of the hose according to FIG. 1, in which the inner surface of the hose wall has unevenness to improve the powder transport;

3 shows a further enlarged detail from the inside of the hose wall of the hose from FIG. 1, in which the unevenness of the inner surface of the hose generated by fibers embedded in the hose material are visible;

Fig. 4 in two partial figures, the tube cross-sections of two different embodiments of tubes according to the invention, in which the electrically conductive particles added to the tube material are evenly distributed over the entire cross-section, in one example (Fig. 4a) for discharging the charges Longitudinally extending line area and in the other example (Fig. 4b) a longitudinally extending stranded conductor are provided;

5 shows in two partial figures the hose cross sections of two further, different embodiments of hoses according to the invention, in which the electrically conductive particles added to the hose material point to an inner region are limited around the inner surface, wherein in one example (FIG. 5a) a plurality of longitudinally extending line regions are provided for discharging the charges and in the other example (FIG. 5b) a plurality of longitudinally extending wires are provided;

Fig. 6 shows the tube cross-sections of two other, different embodiments of tubes according to the invention in two partial figures, in which the electrically conductive particles added to the tube material are introduced into an inner jacket arranged inside the tube, in one example (Fig. 6a) for discharge the charges are provided with a longitudinally extending line region and in the other example (FIG. 6b) a longitudinally extending stranded conductor;

7 shows the cross section through a hose according to another exemplary embodiment, in which a wire or stranded conductor is concentrically surrounded by a local line region which adjoins the inner surface; and

FIG. 8 shows, in a representation comparable to FIG. 7, a further exemplary embodiment, in which a wire or stranded conductor is surrounded by a local line region with a drop-shaped cross section, which only adjoins the inner surface with a tip.

WAYS OF CARRYING OUT THE INVENTION

1 shows a perspective side view of an exemplary hose 10 as it is used for conveying colored powders or the like, and is the subject of the present invention. The hose 10 is usually out an optically transparent polymer, in particular made of polyurethane (PU), polyethylene (PE) or polyvinyl chloride (PVC), or also made of polytetrafluoroethylene (PTFE). But it can also be made of another flexible, electrically insulating material. The hose 10 comprises an annular hose wall 12 which encloses an interior 14. The hose wall 12 is delimited to the interior 14 by an inner surface 13, to the surrounding outer space by an outer surface 11. Exemplary dimensions for the hose are an inner diameter of 10 mm and a thickness of the hose wall of 3 mm. Other dimensions are possible depending on the area of application and the mass flow to be pumped.

The hose 10, particularly when it is used to convey coating powder in the form of a powder-air mixture, has to meet special requirements: The inner surface 13 according to FIG. 2 should have a certain roughness caused by unevenness 15 so that the conveyed Powder does not adhere to the inner surface and can thus impair the conveyance (the unevenness 15 in FIG. 2 is drawn as completely uniform for the sake of simplicity; in reality, however, these unevenness is non-uniform, as can be seen in the detail from FIG. 3). • The electrostatic charges generated when the coating powder or another medium is conveyed on the hose wall 12 should be discharged to earth in a safe manner. • The hose wall 12 should be optically transparent so that the conveying process can be monitored optically. • The hose should be flexible and at the same time kink-proof up to a defined minimum radius. • The hose should have an easy-to-clean, smooth outer surface 11. • The hose should be resistant to abrasion, especially if it is intended to convey powders. • The hose should be resistant to oils and hydrocarbons. • If the hose is used in the area of food production and processing, it must be food-compatible.

These requirements are met in the case of a hose which, for example, consists of PU, PE or PVC as the base material and in which a combination of two electrically conductive devices is provided for dissipating the electrostatic charges. The one electrically conductive device is a region of the tube wall which concentrically surrounds the interior 14 and is delimited by the inner surface 13 and which, by embedding electrically conductive particles in the base material, is provided with a significantly higher electrical conductivity than the base material. The other electrically conductive device is a local electrical conduction element running in the axial direction, which is directly connected to the area of increased electrical conductivity and safely transfers the charges collected through this area to the earth in the axial direction.

The limitation of the area of increased electrical conductivity or the area with the embedded electrically conductive particles by the

Inner surface 13 has the following particular advantage, which is clear from FIG. 3:

3 shows in a greatly enlarged detail a part of the tube wall 12 surrounding the interior 14 with its boundary through the inner surface 13. In the base material of the tube wall 12 (hatched) there are short fibers 16, in particular in the form of carbon fibers, as electrically conductive particles. embedded. The fibers 16 are irregularly distributed and oriented. Due to their elongated shape, which enables contact between two fibers over a greater distance, a comparatively low fiber concentration in the base material results in a significantly increased electrical conductivity. This allows the desired electrical conductivity in the base material to be set without that too many compromises have to be made with regard to the optical transparency of the tube wall 12.

The embedded fibers 16 also have the effect that irregular unevenness 15 is generated in the delimiting inner surface 13, which gives the inner surface 13 a roughness. Since the base material flows around the fibers 16 protruding from the surface, these bumps 15 are rounded. This has the advantage over sharp-edged unevenness, such as occurs, for example, when a soft surface is removed from a mold, that the adherence of conveyed powdery media is reliably avoided, but that the flow behavior is otherwise only influenced to a small extent. In addition, the surface roughness generated by the fibers 16 or other particles can be controlled and adjusted very well in terms of process technology. The base material is preferably a thermoplastic polyurethane (TPU), to which 1 to 3% by weight of carbon fibers are mixed in the area with the increased electrical conductivity.

The two electrically conductive devices connected to one another can now be designed in different ways. Six different exemplary embodiments for their formation are shown in FIGS. 4a, b to 6a, b. The two examples shown in FIG. 4 have in common that the area of increased electrical conductivity extends over the entire cross-sectional area of the tube wall 12. The electrically conductive particles or fibers embedded in the base material are symbolized in FIG. 4 by the crosses within the hatched area.

In the example of FIG. 4a, a line region 17 extending in the axial direction is provided as the electrical line element in the hose wall 12. The line area 17 is comparable to the wall part disclosed in EP-A2-0 974 779 or in US-A-5,170,011 (FIG. 1) and can be produced by filling it with soot or the like. The conduction area 17 discharges the electrical charges to the outside, which are collected by the tube wall 12 made conductive become. Instead of one line area 17, 2 or more line areas can be arranged distributed over the circumference, as can be seen in FIG. 5a for n = 3. The line area 17 extends in the radial direction through the hose wall 12 from the inner surface 13 to the outer surface 11. If direct contact of the line area 17 with the conveyed material in the interior 14 is not desired, the line area can also end in the hose wall, as shown in FIG 5a can be seen.

In the example of FIG. 4b, a wire or stranded conductor 18, which extends in the axial direction and is at a distance from the inner surface 13 in the radial direction, which preferably corresponds to approximately one third of the wall thickness, is provided for discharging the charges into the hose wall 12. A wire strand made of Cu wires, which is reinforced with Kevlar threads, has proven itself as stranded conductor 18. The stranded conductor 18 is embedded directly into the hose wall 12 when the hose 10 is extruded. Instead of the one stranded conductor 18, 2 or more can also be provided distributed over the circumference, as can be seen in the wires 21 from FIG. 5b. The line region 17 or the stranded conductor 18 can run helically in the longitudinal direction around the hose axis in the hose wall 12 for reasons of symmetry.

Since the entire tube wall 12 is filled with electrically conductive particles or fibers in the examples in FIG. 4, the effects of the particle concentration on the optical transparency are particularly great. In addition, the entire hose must be made from the comparatively expensive filled polymer, which leads to increased costs despite the simplified production. These problems can be avoided if the hose has a configuration as shown in the exemplary embodiments in FIGS. 5 and 6. In the examples of FIGS. 5a, b and 6a, b, the area of the hose wall 12 with increased electrical conductivity in the radial direction is limited to a thin inner area 20 (FIG. 5a, b) or inner jacket 22 (FIG. 6a, b) , A tube with a more conductive inner region 20 (cross hatching) can be produced from a corresponding preform, such as this is described in GB-A-1, 041, 255. The inner region 20 has a thickness of 1 mm, for example. 5a, three axial line areas 19 are provided as electrical line elements, which extend from the outer surface 11 through the hose wall 12 to the inner area 20 and are arranged uniformly distributed over the circumference. Instead of the three line areas 19, only one line area can be provided. 5b, a plurality of wires 21 are arranged distributed around the circumference at the boundary between the inner region 20 and the unfilled region of the hose wall. The wires 21 can be part of a braid, which, however, has to be sufficiently loose to maintain the optical transparency.

Of course, a stranded wire can also be used in this case, as in FIG. 4b.

Finally, the two exemplary embodiments in FIG. 6 have an inner jacket 22 as a region with increased electrical conductivity, which is produced during the manufacture of the hose, preferably by coextrusion. Here, too, an axially extending line region 19 or a stranded conductor 18 can again be provided as the electrical line element. In order to make good electrical contact with the inner sheath 22, the stranded conductor 18 is preferably completely enclosed by the material of the inner sheath 22.

Two further exemplary embodiments of the invention are shown in FIGS. 7 and 8. The discharge of the electrostatic charge in the longitudinal direction of the hose 10 takes place here by a wire 21 or stranded conductor 18 with its high conductivity, while the discharge from the inner surface 13 of the

Hose 10 takes place on the wire 21 or stranded conductor 18 through a line region 23 or 24 surrounding the wire 21 or stranded conductor 18, which adjoins the interior 14 of the hose. In the embodiment of FIG. 7, the line area 23 concentrically surrounds the wire 21 or stranded wire 18 and only comes to the surface in a narrowly limited area of the inner surface 13. In the exemplary embodiment in FIG. 8, the line region 24 has a drop-shaped cross section with a tip that points radially inwards and on adjoins the interior 14. Due to the narrowly defined area of the inner surface 13, on which the line area 23, 24 comes to the surface, the risk of caking of powder material conveyed in the hose 10 can be reduced. The risk is particularly low for the line area 24 with the drop-shaped cross section.

The increased electrical conductivity of the tube wall 12 in the line regions 23, 24 is preferably caused by particles which are electrically conductive and are embedded in the base material. The wire 21 or stranded conductor 18 in the hose wall 12 preferably also extends in the longitudinal direction in a helical shape around the hose axis.

The inner surface 13 of the hose 10 is also rough in this case. The roughness is influenced in a controlled manner by the extrusion parameters during the manufacture of the hose 10. In contrast, the outer surface 11 remains smooth, which improves the optical transparency. A further improvement in the optical transparency results from the narrow limitation of the line regions 23 and 24 to the immediate vicinity of the wire 21 or stranded conductor 18.

It has proven particularly useful if the base material of the hose is a polyolefin elastomer.

Overall, the invention results in a hose which is particularly suitable for conveying powders and is distinguished by the following advantages: • The optimally rounded roughness of the inner surface means that minimal delivery pressures can be used, which results in a significant cost reduction since the compressed air required for the promotion is relatively expensive. • Especially in powder coating systems, the new hoses result in better output and a more even application of the powder, despite the reduced delivery pressure. • Due to the conductive areas of the hose wall and the built-in electrical line element (ground wire or strand), a charge or overvoltage generated by friction can be optimally discharged. • The optical transparency of the hose is largely preserved.

LIST OF REFERENCE NUMBERS

10 hose

11 outer surface (hose)

12 hose wall

13 inner surface (hose)

14 interior (hose)

15 bump

16 fibers (electrically conductive, e.g. carbon fiber)

17.19 line area

18 stranded conductors

20 interior

21 wire

22 inner jacket

23.24 line area

Claims

1. hose (10) for conveying electrostatic charges, in particular powdery media, which hose (10) comprises an inner space (14) encircling hose wall (12), which is delimited towards the inner space (14) by an inner surface (13) , wherein the hose wall (12) is constructed from a flexible, electrically poor or non-conductive base material, and wherein at least one electrical line element (17) extending in the longitudinal direction of the hose (10) extends in the longitudinal direction of the hose (10) to discharge electrical charges , 18, 19, 21), characterized in that in the tube cross section at least one area (12, 20, 22, 23, 24) of the tube wall (12) adjacent to the interior (14) of the tube (10) is opposite the Base material has increased electrical conductivity, and that the at least one electrical line element (17, 18, 19, 21) with the area of increased electrical conductivity (12, 20, 2 2, 23, 24) is directly connected.

2. Hose according to claim 1, characterized in that the area with the increased electrical conductivity over the entire

Hose wall (12) extends.

3. Hose according to claim 2, characterized in that the increased electrical conductivity of the hose wall (12) is caused by embedded in the base material, electrically highly conductive particles (16).

4. Hose according to claim 3, characterized in that the base material is an optically transparent polymer, in particular PU, PE or PVC, that short, electrically well conductive fibers (16), in particular carbon fibers, are embedded in the base material as electrically good conductive particles and that the concentration of the fibers (16) is selected so that the tube wall (10) remains optically transparent in the radial direction.

5. Hose according to claim 4, characterized in that about 1 to 3 wt .-% carbon fibers are added to the base material.

6. Hose according to one of claims 2 to 5, characterized in that the at least one electrical line element is designed as a line region (17) embedded in the hose wall (12) with a significantly increased electrical conductivity compared to the base material.

7. Hose according to claim 6, characterized in that the recessed line area (17) is formed in the radial direction through the hose wall (12).

8. Hose according to one of claims 2 to 5, characterized in that the at least one electrical line element as in the hose wall

(12) embedded wire (21) or stranded conductor (18) is formed.

9. Hose according to claim 8, characterized in that the wire or stranded conductor (18) from the inner surface (13) of the hose has a distance which corresponds to approximately one third of the wall thickness of the hose wall (12).

10. Hose according to one of claims 6 to 8, characterized in that the line region (17) or the wire (21) or stranded conductor (18) in the hose wall (12) extends helically in the longitudinal direction around the hose axis.

11. Hose according to claim 1, characterized in that the region with the increased electrical conductivity is limited to a concentric inner region (20) of the hose wall (12) adjoining the inner surface.

12. Hose according to claim 1, characterized in that the area with the increased electrical conductivity is formed by an inner jacket (22) arranged concentrically inside the hose (10).

13. Hose according to claim 11 or 12, characterized in that the increased electrical conductivity in the inner region (20) or in the inner jacket (22) of the hose wall (12) is caused by embedded in the base material, electrically good conductive particles (16).

14. Hose according to claim 13, characterized in that the

The base material of an optically transparent polymer, in particular PU, PE or PVC, is that short, electrically good conductive fibers (16), in particular carbon fibers, are embedded in the base material as electrically good conductive particles, and that the concentration of the fibers (16) and / or the thickness of the inner region (20) or of the inner jacket (22) is selected such that the tube wall (10) remains optically transparent in the radial direction.

15. Hose according to one of claims 11 to 14, characterized in that the at least one electrical line element is designed as a line region (17) embedded in the hose wall (12) with a significantly increased electrical conductivity compared to the base material.

16. Hose according to claim 15, characterized in that the recessed line area (17) in the radial direction from the outer surface (11) to the inner region (20) or inner jacket (22) is continuous.

17. Hose according to one of claims 11 to 14, characterized in that the at least one electrical line element is designed as a wire (21) or stranded conductor (18) embedded in the hose wall (12).

18. Hose according to claim 17, characterized in that the wire (21) or stranded conductor (18) extends at the interface between the inner region (20) or the inner jacket (22) and the rest of the hose wall.

19. Hose according to one of claims 15 to 18, characterized in that the line region (17) or the wire (21) or stranded conductor (18) in the hose wall (12) extends helically in the longitudinal direction around the hose axis.

20. Hose according to claim 1, characterized in that the at least one electrical line element is designed as a wire (21) or stranded conductor (18) embedded in the hose wall (12), that the wire (21) or stranded conductor (18) from the inner surface (13) of the hose (10) is at a distance, and that the area with the increased electrical conductivity is designed as a local line area (23, 24) surrounding the electrical line element (18, 21).

21. Hose according to claim 20, characterized in that the increased electrical conductivity of the hose wall (12) is caused by embedded in the base material, electrically highly conductive particles (16).

22. Hose according to claim 20 or 21, characterized in that the wire (21) or stranded conductor (18) in the hose wall (12) extends in the longitudinal direction helically around the hose axis.

23. Hose according to one of claims 20 to 22, characterized in that the line region (23, 24) surrounding the electrical line element (18, 21) is formed concentrically to the electrical line element (18, 21).

24. Hose according to one of claims 20 to 22, characterized in that the electrical conduction element (18, 21) encircling line region (23, 24) has a teardrop-shaped cross section, which is adjacent to the interior (14) of the hose (10) with a tip.

25. Hose according to one of claims 1 and 20 to 24, characterized in that the base material of the hose is a polyolefin elastomer.

26. Use of a hose according to one of claims 1 to 25 for the promotion of coating powders.